Thermoplastic cigarette wrapper

ABSTRACT

A cigarette wrapper comprising a microporous sheet formed from a cellulose derivative binder filled with finely ground paper. The wrapper also includes a small amount of potassium nitrate. Such cigarette wrappers are effective to selectively reduce the nicotine delivery from normal cigarette tobacco blends.

United States Patent 1 1 Cogbill, II

1 1 THERMOPLASTIC CIGARETTE WRAPPER [75] Inventor: Philip Hancock Cogbill, 11,

Louisville, Ky.

[73} Assignee: Brown & Williamson Tobacco Corporation, Louisville, Ky.

[22] Filed: Dec. 12, 1973 [21] Appl. No.: 426,677

{52] U.S. Cl 131/15 R; 131/2; 162/139 [51] Int. Cl. A24D 01/02 [58] Field of Search ..13l/2,15,17,140144; 162/139 [56] References Cited UNITED STATES PATENTS 2,809,904 10/1957 Korec 131/15 R X 2,840,085 6/1958 Detcrt.... 131/140 R 3,003,895 10/1961 Grunwald 131/17 R 3,070,486 12/1962 Novak 162/139 3,251,368 5/1966 Neurath..... 131/15 R 3,416,537 12/1968 Townend 131/140 C 3,424,169 1/1969 Moren et a1. 131/15 C X 3,477,865 11/1969 Armbrust et al..,.. 131/17 R 3,478,752 11/1969 Briskin et a1 131/2 1 Sept. 30, 1975 OTHER PUBLICATIONS Dangerous Properties of Industrial Materials, by N. Irving Sax, Third Edition, 1968, Pub. by Reinhold Book Pub. Co., N.Y., pp. 960 and 961 cited,

Primary E \'aminerMelvin D. Rein Attorney, Agent, or Firm-Finnegan, Henderson, Farabow and Garrett [5 7] ABSTRACT A cigarette wrapper comprising a microporous sheet formed from a cellulose derivative binder filled with finely ground paper. The wrapper also includes a small amount of potassium nitrate. Such cigarette wrappers are effective to selectively reduce the nicotine delivery from normal cigarette tobacco blends.

32 Claims, N0 Drawings i THERMOPLASTIC CIGARETTE W APPER FIELD OF THE INVENTION The present invention pertains to porous thermoplastic cigarette wrappers which are'effective to selectively reduce the nicotine delivery from normal cigarette tobaccos. More specifically, the present invention pertains to cigarette 'wrapper's comprising a cellulosic binder filled with finely ground paper and a smallamountof potassium nitrate. The filler may also include awhiten er. The present invention also pertains to a smoking article comprising a 'smokeable material contained within the thermoplastic wrapper.

BACKGROUND OF THE INVENTION be able to selectively reduce tar or nicotine delivery,

i.e., to reduce tar ornicotine delivery relative to each other. The cigarette wrapper of the present invention provides means for selectively reducing nicotine delivery.

Tobacco foils prepared from cellulose derivative binders filled with, finely ground tobacco are well known in the art. For example, U.S. Pat. .Nos. 1,716,250; 2,485,670; 2,598,680; 2,706,695; 2,830,597; 2,893,400; 2,897,103; 2,927,588; 2,955,601; 3,062,688; 3,288,148; and 3,343,546 all disclose tobacco foils prepared from finely ground tobacco dispersed in a matrix of-a cellulosic binder. Typical binders include cellulose esters or cellulose ethers such as methyl cellulose, carboxymethyl cellulose, or cellulose acetate. Generally, such tobacco foils are disclosed as useful as cigar wrappers. However, foils prepared from cellulose derivative binders filled with ground tobacco have also been proposed as cigarette wrappers. See German. Offen. 2,008,150.

None of the patents referred to above pertaining to tobacco filled foils suggests substituting a finely ground paper filler forthe finely ground tobacco filler. Certain of the above listed patents (e.g., German Offen. 2,008,150) disclose that the use of the tobacco foils as cigarette wrappers effects a reduction in tar and nicotine delivery. However, none of the prior art recognizes that such wrappers would be effective to selectively reduce nicotine delivery, i.e., decrease the nicotine delivery to a greater degree than the tar delivery; thereby increasing the tar/nicotine ratio. Furthermore, tobacco filled thermosplastic foils have not proven successful as cigarette wrappers. Tobacco filled foils impart a heavy, sour-sweet, or stemmy" off-taste to cigarette tobacco smoke. L

Inclusion of potassium nitrate in cigarette wrappers is also known in the prior art. US. Pat. No. 2,171,986 discloses adding potassium nitrate to conventional paper cigarette wrappers, in combination with certain other nitrogen containing compounds, to produce a mildly alkaline smoke. However, as noted in the patent,

the inclusion of sufficient amounts of potassium nitrate, in the absence of other nitrogen containing compounds, to obtain the desired mildly alkaline smoke adversely affects the ash and burning qualities of the paper. According to the disclosure of this patent, "cigarette paper ordinarily produces an acid smoke, while an alkaline smoke is supposedly less irritating.

A number ofother patents, such as US." Pat. Nos. 1,983,530 and 2,091,598 disclose theacldition of pot'a ss'iurn nitrate, as a combustion "rate accelerator, to cigarette wrappersprepar'ed 'from regenerated cellulose films Neither of thesep'atents suggest that KNO has any effect on tar or nicotine delivery. I

US. Pat. No. 3,699,972 discloses the use 'ofc ombustion-accelerating agents, such'as potassium nitrate, to treat preselected areas of cigarette wrappers'The combustion-accelerating agents cause the treated area of a cigarette wrapper to burn more rapidly than untreated surrounding areas so that increased air flow i's'obtained through the rapid burning areas. While such wrappers are effective to reduce tar and nicotine deliveries, SuCh' wrappers do not'result in selective "nicotine delivery re-' duction. I '5 1 'The porous thermoplastic wrappers of the present invention provide a method of selectively reducing the nicotine delivery from normal cigarette tobacco' blends.'ln addition, unlike tobacco filled wrappers, the thermoplastic wrappers of the present invention do not impart a heavy, sour-sweet, or stemmy off-taste to cigarette tobacco smoke.

In the present invention specification, unless otherwise specified, all references to percentages ,of the various ingredients are by weight, based on the total weight of the composition.

SUMMARY THE INVENTION ethers or mixtures of'cellulose esters and cellulose ethers.

The present invention also contemplates a smoking article 'comprising a smokeable material contained within a cigarette wrapper produced from the above described thin porous thermoplastic sheet.

DESCRIPTION OF PREFERRED EMBODIMENTS:

The type of paper used as a filler in the thermoplastic wrapper of the present invention is not critical. Unfilled flax paper is preferred. Such papers are commerically available and commonly used as plug wraps in the cigarette industry. The paper preferably is ground to a size of mesh or less to insure that it may readily dispersed in the binder.

Amounts of paper greater than about 45 percent by weight normally would not be employed, because at such high paper contents,'the wrapper lacks adequate strength. Amounts of a paper less than about 10 percent are not desirable because the burning'qua'lities of the wrapper are adversely affected. Preferably, the wrapper contains between about 2O percent and about 30 percent by weight finely divided pulverized paper.

The thermoplastic wrapper m'ay'optionally include additional fillers to enhance the whiteness of thesheet. The inclusion of fillers which enhance whiteness is not necessary. However, since cigarette wrappers normally are white, consumers except such an apperance. Accordingly, a white wrapper is desirable to achieve consumer acceptancesuitable whiteners includecalcium carbonate, magnesium carbonate,- aluminum hydroxide, talc, and titanium dioxide. Titanium dioxide, .well known as a white pigment, is the preferred whitener. When whiteners are, included in the wrapper formulation, they maybe added in amounts up to about 40 per.- cent by weight, and preferably in ,amounts of from about percent to. about 30 percent by weight.

The wrappers of the present invention may also include minor amounts of additional fillers, spch as pow-. dered charcoal or powdered alumina. Such fillers may replace part of the finely divided pulverized paper but should not encompass more than about percent by weight of the composition. Largeramounts, should not be employed, as these relatively dense materialsprocess poorly and give a less porous sheet.

The addition of potassium nitrate to the wrapper formulation enhances the selective nicotinereduction effect. In addition, the potassium nitrate acts as a burn accelerator, thereby controlling the puff number of, and reducing delivery of tar from, cigarettes employing the wrapper. v v

Amounts of potassium nitrate greaterthan about 2.8 percent by weight should not be employed. Since the KNO strongly influences the cigarette free'burn rate, larger amounts cause the cigarette to burn too rapidly. At least about 1.5 percent by weightpotassium nitrate should be included in the wrapper formulation to achieve a desired burn 'rate and the beneficial enhanced selective nicotine reduction effect. Preferably, the potassium. nitrate is employed in amounts of from about 1.7 percent to about 2.5 percent by weight.

Oxidizers other than potassium nitrate, such as potassium chlorate sodium chlorate, calcium peroxide and colloidion (cellulose nitrate), are not suitable. When such oxidizers are used in place of potassium nitrate the wrapper becomes too flammable and tends to flame rather than smolder. In addition, such oxidizers are relatively ineffective with respect to controling burn-rate.

The thin porous sheet of the present invention would normally. include at least about 20 percent by weight of a thermoplastic binder. Lesser amounts. of binder are not sufficient to give the sheet adequate integrity. Normally, the sheet would not include more than about 55 percent by weight binder, as larger amounts adversely affect burning characteristics. Preferably, the sheet contains from about 'percent to about 40 percent by weight thermoplastic binder.

Any of the cellulose derivatives employed asbinders' with the tobacco filled foils described in the patent previously referred to are suitable for use with the presentinvention, provided processing techniques are controlled to give the desired degree of porosity. Thesecel: lulose derivatives include various cellulose esters and cellulose ethers, such as methyl cellulose, carboxymethylcellu lose, hydroxyethyl cellulose,.ethyl cellulose. cellulose acetate, etc. A; preferred binder comprisesa mixt'ureof. methyl cellulose and cellulose ace-- tate. Mixtures in which. the cellulose acetate and.

methyl cellulose are presentin ratios offrom 2:1 'to' 20:! parts by weight are particularly preferred.

Suitable cellulose derivatives should-have a sufficient yield, at relatively low-concentrations, relativelyhigh viscosity solutions. In addition, the cellulose derivatives should have a degree of polymerization such that they are capable of forming a coherent, tough sheet or mass when the aqueous or organic solvent is evaporated. The degree of substitution refers to the average number of hydroxyl groups (out if thetotal of three groups) of each glucose unit of the cellulose polymer chain which have had the hydroxyl groups converted to either ester or ether radicals. For example, with respect to methylcellulose, at least 1.6 of the three hydroxyl groups perpoly mer unit must be converted to methoxy groups before the polymer will become water soluble. Methyl cellulose having a degree of substitution greater than 2.0-is decreasingly soluble in water and increasingly soluble in non-polar solvents. Methyl cellulose having a degree of substitution of between about 1.6 and 2.0 is water soluble and also soluble in slightly polar organic solvents. v

To obtain a less brittle and more workable sheet,

from about 2 percent to about 15 percent by weight and preferably from about 6 percent to about 12 per cent by weight, of a plasticizer may be included in the wrapper formulation. Any of thenumerous well known plasticizers suitable for use'with cellulose derivatives may be employed. Specific examples of suitable plastici'zers'are l,3-butylene glycol, propylene glycol, glycerin, butylene glycol, triethylene glycol, etc. A pre ferred plasticizer is a mixture of 1,3-butylene glycol, propylene glycol and glycerin. The wrappers of the present invention may be prepared by adding the binder to the suitable solvent: to produce a swollen, gummy mass. Depending on the nature of the particular binder employed, any number of a wide'variet'y of solvents may be employed. Ground paper is mixed into this mass along with potassium nitrate and, if'desired, a whitener such as titanium dioxide. Additional solvent maybe ad'd'edto the resultant mixture to produce a free flowing slurry. 'lf plasticizers are desired, they may be added to the freeflo wing slurry. The slurry is cast into sheets and dried to removesolvents. The cast sheets should be dried slowly and'at relatively low temperatures so that microporous sheets are produced. lf drying-is effected at a temperature greater than about C; non-porous 'sheets' may result. Y

' Sheets produced according to such' a technique are particularly suitable for use-as cigarette wrappers if process conditions are regulated to attain a thickness which approaches that of conventional cigarette paper. Preferably, the thickness of the sheet should be such that it is no more than fivetimesheavier than conventional-cigarette paper. a 1

The processing technique also should becontrolled so thatthe resultant sheet'has a microporous structure to give a porosity of between about 5 and'6O Greiner,

and preferably between 10 and30 Greiner. As used herein, microporous refers to a sheet in which a majority- (greater than. 50 percent of the pores have a diameter of 3-microns-or less; A porosity within these parameters is importantv with respect to obtaining the properties desired-in a cigarette wrapper, including se lective nicotine reduction. A

Porosity can be controlled within these limits by removing solvent from the cast sheet relatively slowly at relatively low temperatures.(e.g., below 8C.). Specific solvent techniques to achieve the desired porosity depend upon the particularly solvent system employed. Preferably, binders and solvent systems are selected so that drying does not require the use of subatmospheric pressure. a y

The present invention will be further illustrated by the specific examples which follow. These examples are intended to illustrate preferred embodiments and are in no way limiting, I

EXAMPLE I Thermoplasticsheet preparation -7.5 parts by weight methyl cellulose (Dow Methocel 1500)'and 26.8 parts by weight cellulose acetate (Du Pont Plastacelle 09022) are slowly added to 472 parts by weight methylene chloride. The mixture is agitated to insure that all of the binders are completely wet. A swollen gummy mass forms, along with a small amount of free methylene chloride.

26.8 parts by weight titanium dioxide (National Lead Co. Titanox A WD) is added 'to the swollen gummy mass. The titanium dioxide thins the mixture slightly. 26.8 parts by weight paper (Ecusta E-592) which has previously been ground in a Wiley mill and screened to a size less than 140' mesh, is then added to the mixture.

In different batches, varying amounts of KNO is added to the mixture. The amounts are varied from none to amounts sufficient to give, 1.7 percent by weight and 2.1 percent by weight, KNO in the dried sheets.

53 parts by weight methanol are added slowly. The methanol completely dissolves the binder, forming a smooth, free flowing slurry. This mixture is allowed to sit for 30 minutes to an hour to allow the binders to swell.

EXAMPLE 2 Cigarette Preparation-andSmoke Analysis Sheets made in accordance with" Example I were cut into 90 X 29 mm sections'and cigarettes were prepared using these section as wrappers.- Each'cigarette approximately 850 mg. of a commerical cigarette tobacco blend and had a 21 mm. cellulose acetate filter affixed atoneend. A

A number of cigarettes prepared in th'i's'manner were smoked on a smoking machine and the smoke analyzed. The results of the smoke analysis are set forth in Table l. i

The data set forth in Table I demonstrates that the thermoplastic wrappers are effective to selectively reduce nicotine delivery. Relative to the control, allof the thermoplastic wrappers (Samples B. C. and D) resulted in a significant increase in the tar/nicotine ratio. Thus, it is apparent that the wrappers selectively reduced nicotine delivery relative to tar delivery.

As further shown by the data of Table I, in wrappers which included potassium nitrate, the selective nicotine reduction effect was enhanced. Thatthe addition of KNO will enhance selective nicotine reduction is completely unexpected. As noted previously, the prior art has added KNO to conventional cigarette wrappers to obtain a mildly alkaline smoke. Normally, the'addition to tobacco of materials which will render the tobacco smoke more basic, increases nicotine delivery. See Elson et al,]vurnal of the National Caricer Institute, Vol. 48, No. 6, (June 1972) and Elson et al, International Journal of Cancer, Vol. 9 (1972), pp.666-675. Thus,the addition of KNO to the thermoplastic sheets of the present invention produces just the opposite of the expected effect on nicotine delivery, when such sheets are used as cigarette wrappers.

TABLE I TAR/ NO. OF TAR NlCOTlNE H O NlCOTlNE CIGA- RE'I'TES SAMPLE (Mg/cig.) (Mg/Gig.) (Mg./cig.) 'RATlO PUFFS SMOKED A. Control* 12.4 1.01 2.2 12.3 9.0 20 B. Ground Paper Filler 26.0 1.66 6.5 15.6 12.7 90 C. Ground Paper Filler 18.5 1.16 6.9 16.0 9.4 40

1.7% KNO D. Ground Paper Filler 14.3 0.87 3.2 16.4 I 8.0

' 2.1% KNO "Conventional Cigarette Paper E-556 available from Ecusta Paper Division. Olin Mathieson Chemical Corporation The mixture is completed by adding plasticizers in amounts of 4.4 parts by weight 1,3-butylene glycol, 4.4 parts by weight propylene. glycol, and 1.2 parts by weight glycerin. With thicker slurries, it may be necessary to add several drops of a surfactant, such as Span 20 or a defoamer such as SAG 470 to release any entrained air.

The slurry is cast onto a stainless steel sheet using a standard laboratory TLC spreader. The spreader is set for a 1.0 mm thickness sheet.

A commerical hairdryer, which reaches temperatures of 60-70C. is used to remove the solvents. The sheets are dried at low temperatures initially to prevent formation of a non-porous skin: Subsequent to drying, the thermoplastic sheet may be stripped from the stainless steel sheet. The resultant sheet has a color very close to that of normal cigarette paper with a smooth almost soft hand.

Cigarettes'pre'pared from wrappers produced in accordance with Examplel were also smoked by smokers. Subjectively, the smokers found the paper filled thermoplastic wrap to be free of the heavy stemmy offitaste which is obtained from cigarettes prepared from tobacco filled thermoplastic wrappers. The cigarettes prepared from wrappers produced in accordance with Example 1 also gave a uniform char line and a white ash similar to conventional cigarette paper.

EXAMPLE 3 tanium dioxide-ground paper fillter proved to be the most satisfactory.

EXAMPLE 4 To illustrate the potassium nitrate is not effective to selectively reduce nicotine when applied to conventional cigarette paper, a cigarette paper was treated so that it contained about 1.0 percent by weight potassium nitrate. Cigarettes were prepared from this treated paper, as well as from conventional cigarette paper which contains about 1 percent potassium citrate. Both the conventional paper (control) and the paper treated with potassium nitrate 8. The thin, microporous sheet of claim 1 in which said binder is a mixture of methyl cellulose and cellul in which TABLE I1 WRAPPER FORMULATlONS Fillers Oxidizer Parts by Weight Parts by Wt. Titanium Finely Ground Potassium Dioxide Paper Fiber (E-592) Other Nitrate 1 26.8 26.8 2.1 11 26.8 13.4 13.4 Powdered 2.1

Charcoal (Norit A) 1 [ll 26.8 l3.4 [3.4 Powdered Alumina 2.]

(Reynolds Metals RH-3l TABLE III lose acetate.

9. The thin,,microporous sheet of claim 8 in which Nicotine Tar Nic Puffs the ratio of cellulose acetate to rnethyl cellulose is be- 30 tween 2:l and 20:1 parts by weight. gonveritionaldC ligail'ettled 10. The thin, microporous sheet of claim 1 which has I I t V 3 3 u c 14.8 3'6 092 70 a porosity of betw een about 5 and 60 Greiner. I Control 11. The thin, microporous sheet of clalm WhlCll K C'tmte L02 has a porosity between about l0 and Greiner.

were formed into cigarettes and smoked on a smoke testing machine. Results of the analyses of the smoke are set forth in Table III. As is apparent from the data in this table, potassium nitrate on normal cigarette paper is not effective to selectively reduce nicotine.

Those skilled in the art will visualize many modifications and variations of the invention set forth above without departing from its spirit and scope. Accordingly, while the preferred embodiments of the invention have been described, it is understood that the invention is not confined to the specifics set forth by way of illustration.

What is claimed is:

1. A thin, microporous cigarette wrapper sheet comprising:

a. about 10 percent to about 45 percent by weight finely divided unfilled flax paper having a size of 140 mesh or less;

b. about 1.5 percent to about 2.8 percent by Weight potassium nitrate;

c. up to about percent by weight of a whitener;

and

d. about 20 percent to about 55 percent by weight of a thermoplastic binder selected from the group consisting of cellulose esters, cellulose ethers, and mixtures thereof.

2. The thin, microporous sheet of claim 1 which comprises about 20 percent to about 20 percent by weight of said finely divided paper.

3. The thin, microporous sheet of claim 1 which comprises about 1.7 percent to about 2.5 percent by weight of said potassium nitrate.

4. The thin, microporous sheet of claim 1 which com- 12. The thin, microporous sheet of claim. 1 which includes from about 2 percent to about 15 percent by weight of a plasticizer.

,13. The thin, microporous sheet of claim 12 which includes from about 6 percent to about 12 percent by weight of a plasticizer.

14. The thin, microporous sheet of claim 12 in which said plasticizer is a mixture of 1,3-butylene glycol, propylene glycol and glycerin.

15. The thin, microporous sheet of claim 1 in which at least 50% of'the pores of said sheet have a diameter of no more than 3 microns.

16. A thin, microporous cigarette wrapper sheet having a porosity of between about l0-3O Greiner and in which at least SOpercent of the pores of said sheet have a diameter of no more than 3 microns said sheet comprising:

a. about 20 percent to about 30 percent by weight finely divided unfilled flax paper having a size of mesh or less;

b. about l".7 percent to about 2.5 percent by weight potassium nitrate; 1

c. about 15 percent to about 3O percent by weight titanium dioxide;

d. about 2 percent to about 15 percent by weight of a plasticizer; and

e. about 30 percent to about 40 percent by weight of a thermoplastic binder selected from the group consisting of cellulose esters, cellulose ethers and mixtures thereof. E

17. The thin, microporous sheet of claim 16 in which said binder comprises from 2 to 20 parts by weight cellulose acetate and one part by weight methyl cellulose.

18. A smoking article comprising a smokeable mate rial contained within the thin, microporous sheet of claim 16.

19. A smoking article comprising a smokeable material contained within a thin, microporous cigarette wrapper which wrapper comprises:

a. about 10 percent to about 45 percent by weight finely divided unfilled flax paper having a size of l4O mesh or less;

b. about 1.5 percent to about 2.8 percent by weight potassium nitrate;

c. up to about 40 percent by weight of a whitener;

and

d. about 20 percent to about 55 percent by weight of a thermoplastic binder selected from the group consisting of cellulose esters, cellulose ethers and mixtures thereof.

20. The smoking article of claim 19 in which said wrapper comprises about 20 percent to about 30 percent by weight of said finely divided paper.

21. The smoking article of claim 18 in which said wrapper comprises about 1.7 percent to about 2.5 percent by weight of said potassium nitrate.

22. The smoking article of claim 19 in which said wrapper comprises about percent to about 30 percent by weight of said whitener.

23. The smoking article of claim 19 in which said whitener of said wrapper is selected from the group consisting of calcium carbonate, magnesium carbonate, aluminum hydroxide, talc, and titanium dioxide.

24. The smoking article of claim 23 in which said whitener is titanium dioxide.

25. The smoking article of claim 19 in which said wrapper comprises about 30 percent to about 40 percent by weight of said binder.

26. The smoking article of claim 19 in which said binder of said wrapper comprises a mixture of methyl cellulose and cellulose acetate.

27. The smoking article of claim 19 in which said wrapper has a porosity of between about 5 and to about 60 Greiner.

28. The smoking article of claim 27 in which said wrapper has a porosity of between about 10 and about 30 Greiner.

29. The smoking article of claim 19 in which said wrapper includes from about 2 percent to about 15 percent by weight of a plasticizer.

30. The smoking article of claim 29 which includes from about 6 percent to about 12 percent by weight of a plasticizer.

31. The smoking article of claim 29 in which said plasticizer comprises a mixture of 1,3-butylene glycol, propylene glycol and glycerin.

32. The smoking article of claim 19 in which at least 50 percent of the pores of said sheet have a diameter of no more than 3 microns.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,908,671 Dated September 30, 1975 Inventor(s) Philip Hancock Cogbill, II

It is certified that error appears in the above-identified patent Q and that said Letters Patent are hereby corrected as shown below:

Column 2, line 26, delete "invention".

Column 2, line 54, after "may" insert be--. 9

Column 2, lines 60-61, after "percent" insert by weight-.

Column 3, line 1, delete "except" and insert therefor expect---.

0 Column 3, line I, delete "apperance" and insert therefor appearance.

Column 4 line 60, after "percent" immediately add Column 4, line 67, delete "8" and insert therefor ----80---. C

Column 4, line 68, after "solvent" insert removal-.

Column 6, line 6, after "cigarette" insert contained.

Column 7, line 1, delete "fillter" and insert therefor O --filler-.

Column 7, line 5, delete "the" and insert therefor -that-.

Claim 2, line 2, change "20 percent" (second occurence) to --30 percent-. O

Claim 21, line 1, delete "1,8" and insert therefor -l9-.

Claim 27, line 2 delete "to".

g Signed and Scaled this [SEAL] tenth D3) of February 1976 Arrest:

RUTH C, MASON Allflting Officer C. MARSHALL DANN nmmissimzer uj'larents and Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 908, 671 Dated September 30 1975 Inventor(s) Philip Hancock Cogbill, II

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 2, line 2, change "20 percent" (second occurrence) to -30 percent-.

Claim 21, line 1, delete "l8" and insert therefor--l9.

Claim 27, line 2, delete "to".

Signed and Sealed this sixteenth Day Of December 1975 [SEAL] RUTH. C. MRSON C. MARSHALL DANN Alleslmg Ojjlcer (ommissinner nfPatents and Trademarks 

1. A THIN, MICROPOROUS CIGARETTE WRAPPER SHEET COMPRISING: A. ABOUT 10 PERCENT TO ABOUT 45 PERCENT BY WEIGHT FINELY DIVIDED UNFILLED FLAX PAPER HAVING A SIZE OF 140 MESH OR LESS, B. ABOUT 1.5 PERCENT TO ABOUT 2.8 PERCENT BY WEIGHT POTASSIUM NITRATE, C. UP TO ABOUT 40 PERCENT BY WEIGHT OF A WHITENER, AND D. ABOUT 20 PERCENT TO ABOUT 55 PERCENT BY WEIGHT OF A THERMOPLASTIC BINDER SELECTED FROM THE GROUP CONSISTING OF CELLULOSE ESTERS, CELLULOSE ETHERS, AND MIXTURES THEREOF.
 2. The thin, microporous sheet of claim 1 which comprises about 20 percent to about 20 percent by weight of said finely divided paper.
 3. The thin, microporous sheet of claim 1 which comprises about 1.7 percent to about 2.5 percent by weight of said potassium nitrate.
 4. The thin, microporous sheet of claim 1 which comprises about 15 percent to about 30 percent by weight of said whitener.
 5. The thin, microporous sheet of claim 1 in which said whitener is selected from the group consisting of calcium carbonate, magnesium carbonate, aluminum hydroxide, talc, and titanium dioxide.
 6. The thin, microporous sheet of claim 1 in which said whitener is titanium dioxide.
 7. The thin, microporous sheet of claim 1 which comprises about 30 percent to about 40 percent by weight of said binder.
 8. The thin, microporous sheet of claim 1 in which said binder is a mixture of methyl cellulose and cellulose acetate.
 9. The thin, microporous sheet of claim 8 in which the ratio of cellulose acetate to methyl cellulose is between 2:1 and 20:1 parts by weight.
 10. The thin, microporous sheet of claim 1 which has a porosity of between about 5 and 60 Greiner.
 11. The thin, microporous sheet of claim 10 which has a porosity between about 10 and 30 Greiner.
 12. The thin, microporous sheet of claim 1 which includes from about 2 percent to about 15 percent by weight of a plasticizer.
 13. The thin, microporous sheet of claim 12 which includes from about 6 percent to about 12 percent by weight of a plasticizer.
 14. The thin, microporous sheet of claim 12 in which said plasticizer is a mixture of 1,3-butylene glycol, propylene glycol and glycerin.
 15. The thin, microporous sheet of claim 1 in which at least 50% of the pores of said sheet have a diameter of no more than 3 microns.
 16. A thin, microporous cigarette wrapper sheet having a porosity of between about 10-30 Greiner and in which at least 50 percent of the pores of said sheet have a diameter of no more than 3 microns said sheet comprising: a. about 20 percent to about 30 percent by weight finely divided unfilled flax paper having a size of 140 mesh or less; b. about 1.7 percent to about 2.5 percent by weight potassium nitrate; c. about 15 percent to about 30 percent by weight titanium dioxide; d. about 2 percent to about 15 percent by weight of a plasticizer; and e. about 30 percent to about 40 percent by weight of a thermoplastic binder selected from the group consisting of cellulose esters, cellulose ethers and mixtures thereof.
 17. The thin, microporous sheet of claim 16 in which said binder comprises from 2 to 20 parts by weight cellulose acetate and one part by weight methyl cellulose.
 18. A smoking article comprising a smokeable material contained within the thin, microporous sheet of claim
 16. 19. A smoking article comprising a smokeable material contained within a thin, microporous cigarette wrapper which wrapper comprises: a. about 10 percent to about 45 percent by weight finely divided unfilled flax paper having a size of 140 mesh or less; b. about 1.5 percent to about 2.8 percent by weight potassium nitrate; c. up to about 40 percent by weight of a whitener; and d. about 20 percent to about 55 percent by weight of a thermoplastic binder selected from the group consisting of cellulose esters, cellulose ethers and mixtures thereof.
 20. The smoking article of claim 19 in which said wrapper comprises about 20 percent to about 30 percent by weight of said finely divided paper.
 21. The smoking article of claim 18 in which said wrapper comprises about 1.7 percent to about 2.5 percent by weight of said potassium nitrate.
 22. The smoking article of claim 19 in which said wrapper comprises about 15 percent to about 30 percent by weight of said whitener.
 23. The smoking article of claim 19 in which said whitener of said wrapper is selected from the group consisting of calcium carbonate, magnesium carbonate, aluminum hydroxide, talc, and titanium dioxide.
 24. The smoking article of claim 23 in which said whitener is titanium dioxide.
 25. The smoking article of claim 19 in which said wrapper comprises about 30 percent to about 40 percent by weight of said binder.
 26. The smoking article of claim 19 in which said binder of said wrapper comprises a mixture of methyl cellulose and cellulose acetate.
 27. The smoking article of claim 19 in which said wrapper has a porosity of between about 5 and to about 60 Greiner.
 28. The smoking article of claim 27 in which said wrapper has a porosity of between about 10 and about 30 Greiner.
 29. The smoking article of claim 19 in which said wrapper includes from about 2 percent to about 15 percent by weight of a plasticizer.
 30. The smoking article of claim 29 which includes from about 6 percent to about 12 percent by weight of a plasticizer.
 31. The smoking article of claim 29 in which said plasticizer comprises a mixture of 1,3-butylene glycol, propylene glycol and glycerin.
 32. The smoking article of claim 19 in which at least 50 percent of the pores of said sheet have a diameter of no more than 3 microns. 